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9 Commits

Author SHA1 Message Date
Peter Lieven
e22492d332 ui/vnc: disable adaptive update calculations if not needed
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Peter Lieven
919372251c ui/vnc: optimize setting in vnc_dpy_update()
Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Peter Lieven
863d7c9105 ui/vnc: optimize clearing in find_and_clear_dirty_height()
The following artifical test (just the bitmap operation part) running
vnc_update_client 65536 times on a 2560x2048 surface illustrates the
performance difference:

All bits clean - vnc_update_client_new: 0.07 secs
                 vnc_update_client_new2: 0.07 secs
                 vnc_update_client_old: 10.98 secs

All bits dirty - vnc_update_client_new: 11.26 secs
               - vnc_update_client_new2: 0.29 secs
                 vnc_update_client_old: 20.19 secs

Few bits dirty - vnc_update_client_new: 0.07 secs
               - vnc_update_client_new2: 0.07 secs
                 vnc_update_client_old: 10.98 secs

vnc_update_client_new2 shows the performance of vnc_update_client
with this patch added.

Comparing with the test run of the last patch the performance
is at least unchanged while it is significantly improved
for the all bits dirty case.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Peter Lieven
12b316d4c1 ui/vnc: optimize dirty bitmap tracking
vnc_update_client currently scans the dirty bitmap of each client
bitwise which is a very costly operation if only few bits are dirty.
vnc_refresh_server_surface does almost the same.
this patch optimizes both by utilizing the heavily optimized
function find_next_bit to find the offset of the next dirty
bit in the dirty bitmaps.

The following artifical test (just the bitmap operation part) running
vnc_update_client 65536 times on a 2560x2048 surface illustrates the
performance difference:

All bits clean - vnc_update_client_new: 0.07 secs
 vnc_update_client_old: 10.98 secs

All bits dirty - vnc_update_client_new: 11.26 secs
 vnc_update_client_old: 20.19 secs

Few bits dirty - vnc_update_client_new: 0.08 secs
 vnc_update_client_old: 10.98 secs

The case for all bits dirty is still rather slow, this
is due to the implementation of find_and_clear_dirty_height.
This will be addresses in a separate patch.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Peter Lieven
6cd859aa8a ui/vnc: derive cmp_bytes from VNC_DIRTY_PIXELS_PER_BIT
this allows for setting VNC_DIRTY_PIXELS_PER_BIT to different
values than 16 if desired.

Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Peter Lieven
b4c85ddcec ui/vnc: introduce VNC_DIRTY_PIXELS_PER_BIT macro
Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Gerd Hoffmann
38ee14f4f3 vnc: fix use-after-free in vnc_update_client_sync
Spotted by Coverity:

876     static int vnc_update_client_sync(VncState *vs, int has_dirty)
877     {

(1) Event freed_arg:    "vnc_update_client(VncState *, int)" frees "vs".  [details]
Also see events:        [deref_arg]

878         int ret = vnc_update_client(vs, has_dirty);

(2) Event deref_arg:    Calling "vnc_jobs_join(VncState *)" dereferences freed pointer "vs". [details]
Also see events:        [freed_arg]

879         vnc_jobs_join(vs);
880         return ret;
881     }

Remove vnc_update_client_sync wrapper, replace it with an additional
argument to vnc_update_client, so we can so the sync properly in
vnc_update_client (i.e. skip it in case of a client disconnect).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
2014-03-10 12:35:04 +01:00
Gonglei (Arei)
e3c1adf16e vnc: Fix qemu crashed when vnc client disconnect suddenly
Hi,

When I use RealVNC viewer client (http://www.realvnc.com/) to connect vnc server,
the client disconnect suddenly, and I click reconnect button immediately, then the Qemu crashed.

In the function vnc_worker_thread_loop, will call vnc_async_encoding_start
to set the local vs->output buffer by global queue's buffer. Then send rectangles to
the vnc client call function vnc_send_framebuffer_update. Finally, Under normal circumstances,
call vnc_async_encoding_end to set the global queue'buffer by the local vs->output conversely.

When the vnc client disconnect, the job->vs->csock will be set to -1. And the current prcoess
logic will goto disconnected partion without call function vnc_async_encoding_end.
But, the function vnc_send_framebuffer_update will call buffer_reserve, which
maybe call g_realloc reset the local vs's buffer, meaning the global queue's buffer is modified also.
If anyone use the original global queue's buffer memory will cause corruption and then crash qemu.

This patch assure the function vnc_async_encoding_end being called
even though the vnc client disconnect suddenly.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
Markus Armbruster
2e7bcdb99a vnc: Fix tight_detect_smooth_image() for lossless case
VncTight member uint8_t quality is either (uint8_t)-1 for lossless or
less than 10 for lossy.

tight_detect_smooth_image() first promotes it to int, then compares
with -1.  Always unequal, so we always execute the lossy code.  Reads
beyond tight_conf[] and returns crap when quality is actually
lossless.

Compare to (uint8_t)-1 instead, like we do elsewhere.

Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2014-03-10 12:35:04 +01:00
4 changed files with 141 additions and 103 deletions

View File

@@ -330,7 +330,7 @@ tight_detect_smooth_image(VncState *vs, int w, int h)
} else {
errors = tight_detect_smooth_image16(vs, w, h);
}
if (quality != -1) {
if (quality != (uint8_t)-1) {
return (errors < tight_conf[quality].jpeg_threshold);
}
return (errors < tight_conf[compression].gradient_threshold);

View File

@@ -252,6 +252,8 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
if (job->vs->csock == -1) {
vnc_unlock_display(job->vs->vd);
/* Copy persistent encoding data */
vnc_async_encoding_end(job->vs, &vs);
goto disconnected;
}
@@ -278,6 +280,9 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
vnc_async_encoding_end(job->vs, &vs);
qemu_bh_schedule(job->vs->bh);
} else {
/* Copy persistent encoding data */
vnc_async_encoding_end(job->vs, &vs);
}
vnc_unlock_output(job->vs);

227
ui/vnc.c
View File

@@ -417,8 +417,7 @@ out_error:
3) resolutions > 1024
*/
static int vnc_update_client(VncState *vs, int has_dirty);
static int vnc_update_client_sync(VncState *vs, int has_dirty);
static int vnc_update_client(VncState *vs, int has_dirty, bool sync);
static void vnc_disconnect_start(VncState *vs);
static void vnc_colordepth(VncState *vs);
@@ -431,29 +430,25 @@ static int vnc_refresh_server_surface(VncDisplay *vd);
static void vnc_dpy_update(DisplayChangeListener *dcl,
int x, int y, int w, int h)
{
int i;
VncDisplay *vd = container_of(dcl, VncDisplay, dcl);
struct VncSurface *s = &vd->guest;
int width = surface_width(vd->ds);
int height = surface_height(vd->ds);
h += y;
/* round x down to ensure the loop only spans one 16-pixel block per,
iteration. otherwise, if (x % 16) != 0, the last iteration may span
two 16-pixel blocks but we only mark the first as dirty
*/
w += (x % 16);
x -= (x % 16);
/* this is needed this to ensure we updated all affected
* blocks if x % VNC_DIRTY_PIXELS_PER_BIT != 0 */
w += (x % VNC_DIRTY_PIXELS_PER_BIT);
x -= (x % VNC_DIRTY_PIXELS_PER_BIT);
x = MIN(x, width);
y = MIN(y, height);
w = MIN(x + w, width) - x;
h = MIN(h, height);
h = MIN(y + h, height);
for (; y < h; y++)
for (i = 0; i < w; i += 16)
set_bit((x + i) / 16, s->dirty[y]);
for (; y < h; y++) {
bitmap_set(s->dirty[y], x / VNC_DIRTY_PIXELS_PER_BIT,
DIV_ROUND_UP(w, VNC_DIRTY_PIXELS_PER_BIT));
}
}
void vnc_framebuffer_update(VncState *vs, int x, int y, int w, int h,
@@ -571,6 +566,15 @@ void *vnc_server_fb_ptr(VncDisplay *vd, int x, int y)
ptr += x * VNC_SERVER_FB_BYTES;
return ptr;
}
/* this sets only the visible pixels of a dirty bitmap */
#define VNC_SET_VISIBLE_PIXELS_DIRTY(bitmap, w, h) {\
int y;\
memset(bitmap, 0x00, sizeof(bitmap));\
for (y = 0; y < h; y++) {\
bitmap_set(bitmap[y], 0,\
DIV_ROUND_UP(w, VNC_DIRTY_PIXELS_PER_BIT));\
} \
}
static void vnc_dpy_switch(DisplayChangeListener *dcl,
DisplaySurface *surface)
@@ -596,7 +600,9 @@ static void vnc_dpy_switch(DisplayChangeListener *dcl,
qemu_pixman_image_unref(vd->guest.fb);
vd->guest.fb = pixman_image_ref(surface->image);
vd->guest.format = surface->format;
memset(vd->guest.dirty, 0xFF, sizeof(vd->guest.dirty));
VNC_SET_VISIBLE_PIXELS_DIRTY(vd->guest.dirty,
surface_width(vd->ds),
surface_height(vd->ds));
QTAILQ_FOREACH(vs, &vd->clients, next) {
vnc_colordepth(vs);
@@ -604,7 +610,9 @@ static void vnc_dpy_switch(DisplayChangeListener *dcl,
if (vs->vd->cursor) {
vnc_cursor_define(vs);
}
memset(vs->dirty, 0xFF, sizeof(vs->dirty));
VNC_SET_VISIBLE_PIXELS_DIRTY(vs->dirty,
surface_width(vd->ds),
surface_height(vd->ds));
}
}
@@ -751,7 +759,7 @@ static void vnc_dpy_copy(DisplayChangeListener *dcl,
QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
if (vnc_has_feature(vs, VNC_FEATURE_COPYRECT)) {
vs->force_update = 1;
vnc_update_client_sync(vs, 1);
vnc_update_client(vs, 1, true);
/* vs might be free()ed here */
}
}
@@ -770,11 +778,12 @@ static void vnc_dpy_copy(DisplayChangeListener *dcl,
y = dst_y + h - 1;
inc = -1;
}
w_lim = w - (16 - (dst_x % 16));
if (w_lim < 0)
w_lim = w - (VNC_DIRTY_PIXELS_PER_BIT - (dst_x % VNC_DIRTY_PIXELS_PER_BIT));
if (w_lim < 0) {
w_lim = w;
else
w_lim = w - (w_lim % 16);
} else {
w_lim = w - (w_lim % VNC_DIRTY_PIXELS_PER_BIT);
}
for (i = 0; i < h; i++) {
for (x = 0; x <= w_lim;
x += s, src_row += cmp_bytes, dst_row += cmp_bytes) {
@@ -782,10 +791,11 @@ static void vnc_dpy_copy(DisplayChangeListener *dcl,
if ((s = w - w_lim) == 0)
break;
} else if (!x) {
s = (16 - (dst_x % 16));
s = (VNC_DIRTY_PIXELS_PER_BIT -
(dst_x % VNC_DIRTY_PIXELS_PER_BIT));
s = MIN(s, w_lim);
} else {
s = 16;
s = VNC_DIRTY_PIXELS_PER_BIT;
}
cmp_bytes = s * VNC_SERVER_FB_BYTES;
if (memcmp(src_row, dst_row, cmp_bytes) == 0)
@@ -793,7 +803,8 @@ static void vnc_dpy_copy(DisplayChangeListener *dcl,
memmove(dst_row, src_row, cmp_bytes);
QTAILQ_FOREACH(vs, &vd->clients, next) {
if (!vnc_has_feature(vs, VNC_FEATURE_COPYRECT)) {
set_bit(((x + dst_x) / 16), vs->dirty[y]);
set_bit(((x + dst_x) / VNC_DIRTY_PIXELS_PER_BIT),
vs->dirty[y]);
}
}
}
@@ -862,35 +873,24 @@ static int find_and_clear_dirty_height(struct VncState *vs,
int h;
for (h = 1; h < (height - y); h++) {
int tmp_x;
if (!test_bit(last_x, vs->dirty[y + h])) {
break;
}
for (tmp_x = last_x; tmp_x < x; tmp_x++) {
clear_bit(tmp_x, vs->dirty[y + h]);
}
bitmap_clear(vs->dirty[y + h], last_x, x - last_x);
}
return h;
}
static int vnc_update_client_sync(VncState *vs, int has_dirty)
{
int ret = vnc_update_client(vs, has_dirty);
vnc_jobs_join(vs);
return ret;
}
static int vnc_update_client(VncState *vs, int has_dirty)
static int vnc_update_client(VncState *vs, int has_dirty, bool sync)
{
if (vs->need_update && vs->csock != -1) {
VncDisplay *vd = vs->vd;
VncJob *job;
int y;
int width, height;
int height;
int n = 0;
if (vs->output.offset && !vs->audio_cap && !vs->force_update)
/* kernel send buffers are full -> drop frames to throttle */
return 0;
@@ -906,33 +906,27 @@ static int vnc_update_client(VncState *vs, int has_dirty)
*/
job = vnc_job_new(vs);
width = MIN(pixman_image_get_width(vd->server), vs->client_width);
height = MIN(pixman_image_get_height(vd->server), vs->client_height);
for (y = 0; y < height; y++) {
int x;
int last_x = -1;
for (x = 0; x < width / 16; x++) {
if (test_and_clear_bit(x, vs->dirty[y])) {
if (last_x == -1) {
last_x = x;
}
} else {
if (last_x != -1) {
int h = find_and_clear_dirty_height(vs, y, last_x, x,
height);
n += vnc_job_add_rect(job, last_x * 16, y,
(x - last_x) * 16, h);
}
last_x = -1;
}
}
if (last_x != -1) {
int h = find_and_clear_dirty_height(vs, y, last_x, x, height);
n += vnc_job_add_rect(job, last_x * 16, y,
(x - last_x) * 16, h);
y = 0;
for (;;) {
int x, h;
unsigned long x2;
unsigned long offset = find_next_bit((unsigned long *) &vs->dirty,
height * VNC_DIRTY_BPL(vs),
y * VNC_DIRTY_BPL(vs));
if (offset == height * VNC_DIRTY_BPL(vs)) {
/* no more dirty bits */
break;
}
y = offset / VNC_DIRTY_BPL(vs);
x = offset % VNC_DIRTY_BPL(vs);
x2 = find_next_zero_bit((unsigned long *) &vs->dirty[y],
VNC_DIRTY_BPL(vs), x);
bitmap_clear(vs->dirty[y], x, x2 - x);
h = find_and_clear_dirty_height(vs, y, x, x2, height);
n += vnc_job_add_rect(job, x * VNC_DIRTY_PIXELS_PER_BIT, y,
(x2 - x) * VNC_DIRTY_PIXELS_PER_BIT, h);
}
vnc_job_push(job);
@@ -940,8 +934,11 @@ static int vnc_update_client(VncState *vs, int has_dirty)
return n;
}
if (vs->csock == -1)
if (vs->csock == -1) {
vnc_disconnect_finish(vs);
} else if (sync) {
vnc_jobs_join(vs);
}
return 0;
}
@@ -1846,7 +1843,7 @@ static void framebuffer_update_request(VncState *vs, int incremental,
int w, int h)
{
int i;
const size_t width = surface_width(vs->vd->ds) / 16;
const size_t width = surface_width(vs->vd->ds) / VNC_DIRTY_PIXELS_PER_BIT;
const size_t height = surface_height(vs->vd->ds);
if (y_position > height) {
@@ -2548,7 +2545,9 @@ static int vnc_refresh_lossy_rect(VncDisplay *vd, int x, int y)
vs->lossy_rect[sty][stx] = 0;
for (j = 0; j < VNC_STAT_RECT; ++j) {
bitmap_set(vs->dirty[y + j], x / 16, VNC_STAT_RECT / 16);
bitmap_set(vs->dirty[y + j],
x / VNC_DIRTY_PIXELS_PER_BIT,
VNC_STAT_RECT / VNC_DIRTY_PIXELS_PER_BIT);
}
has_dirty++;
}
@@ -2652,8 +2651,8 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
int width = pixman_image_get_width(vd->guest.fb);
int height = pixman_image_get_height(vd->guest.fb);
int y;
uint8_t *guest_row;
uint8_t *server_row;
uint8_t *guest_row0 = NULL, *server_row0;
int guest_stride = 0, server_stride;
int cmp_bytes;
VncState *vs;
int has_dirty = 0;
@@ -2671,47 +2670,64 @@ static int vnc_refresh_server_surface(VncDisplay *vd)
* Check and copy modified bits from guest to server surface.
* Update server dirty map.
*/
cmp_bytes = 64;
cmp_bytes = VNC_DIRTY_PIXELS_PER_BIT * VNC_SERVER_FB_BYTES;
if (cmp_bytes > vnc_server_fb_stride(vd)) {
cmp_bytes = vnc_server_fb_stride(vd);
}
if (vd->guest.format != VNC_SERVER_FB_FORMAT) {
int width = pixman_image_get_width(vd->server);
tmpbuf = qemu_pixman_linebuf_create(VNC_SERVER_FB_FORMAT, width);
} else {
guest_row0 = (uint8_t *)pixman_image_get_data(vd->guest.fb);
guest_stride = pixman_image_get_stride(vd->guest.fb);
}
guest_row = (uint8_t *)pixman_image_get_data(vd->guest.fb);
server_row = (uint8_t *)pixman_image_get_data(vd->server);
for (y = 0; y < height; y++) {
if (!bitmap_empty(vd->guest.dirty[y], VNC_DIRTY_BITS)) {
int x;
uint8_t *guest_ptr;
uint8_t *server_ptr;
server_row0 = (uint8_t *)pixman_image_get_data(vd->server);
server_stride = pixman_image_get_stride(vd->server);
if (vd->guest.format != VNC_SERVER_FB_FORMAT) {
qemu_pixman_linebuf_fill(tmpbuf, vd->guest.fb, width, 0, y);
guest_ptr = (uint8_t *)pixman_image_get_data(tmpbuf);
} else {
guest_ptr = guest_row;
}
server_ptr = server_row;
for (x = 0; x + 15 < width;
x += 16, guest_ptr += cmp_bytes, server_ptr += cmp_bytes) {
if (!test_and_clear_bit((x / 16), vd->guest.dirty[y]))
continue;
if (memcmp(server_ptr, guest_ptr, cmp_bytes) == 0)
continue;
memcpy(server_ptr, guest_ptr, cmp_bytes);
if (!vd->non_adaptive)
vnc_rect_updated(vd, x, y, &tv);
QTAILQ_FOREACH(vs, &vd->clients, next) {
set_bit((x / 16), vs->dirty[y]);
}
has_dirty++;
}
y = 0;
for (;;) {
int x;
uint8_t *guest_ptr, *server_ptr;
unsigned long offset = find_next_bit((unsigned long *) &vd->guest.dirty,
height * VNC_DIRTY_BPL(&vd->guest),
y * VNC_DIRTY_BPL(&vd->guest));
if (offset == height * VNC_DIRTY_BPL(&vd->guest)) {
/* no more dirty bits */
break;
}
guest_row += pixman_image_get_stride(vd->guest.fb);
server_row += pixman_image_get_stride(vd->server);
y = offset / VNC_DIRTY_BPL(&vd->guest);
x = offset % VNC_DIRTY_BPL(&vd->guest);
server_ptr = server_row0 + y * server_stride + x * cmp_bytes;
if (vd->guest.format != VNC_SERVER_FB_FORMAT) {
qemu_pixman_linebuf_fill(tmpbuf, vd->guest.fb, width, 0, y);
guest_ptr = (uint8_t *)pixman_image_get_data(tmpbuf);
} else {
guest_ptr = guest_row0 + y * guest_stride;
}
guest_ptr += x * cmp_bytes;
for (; x < DIV_ROUND_UP(width, VNC_DIRTY_PIXELS_PER_BIT);
x++, guest_ptr += cmp_bytes, server_ptr += cmp_bytes) {
if (!test_and_clear_bit(x, vd->guest.dirty[y])) {
continue;
}
if (memcmp(server_ptr, guest_ptr, cmp_bytes) == 0) {
continue;
}
memcpy(server_ptr, guest_ptr, cmp_bytes);
if (!vd->non_adaptive) {
vnc_rect_updated(vd, x * VNC_DIRTY_PIXELS_PER_BIT,
y, &tv);
}
QTAILQ_FOREACH(vs, &vd->clients, next) {
set_bit(x, vs->dirty[y]);
}
has_dirty++;
}
y++;
}
qemu_pixman_image_unref(tmpbuf);
return has_dirty;
@@ -2734,7 +2750,7 @@ static void vnc_refresh(DisplayChangeListener *dcl)
vnc_unlock_display(vd);
QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
rects += vnc_update_client(vs, has_dirty);
rects += vnc_update_client(vs, has_dirty, false);
/* vs might be free()ed here */
}
@@ -3134,7 +3150,9 @@ void vnc_display_open(DisplayState *ds, const char *display, Error **errp)
acl = 1;
#endif
} else if (strncmp(options, "lossy", 5) == 0) {
#ifdef CONFIG_VNC_JPEG
vs->lossy = true;
#endif
} else if (strncmp(options, "non-adaptive", 12) == 0) {
vs->non_adaptive = true;
} else if (strncmp(options, "share=", 6) == 0) {
@@ -3151,6 +3169,13 @@ void vnc_display_open(DisplayState *ds, const char *display, Error **errp)
}
}
/* adaptive updates are only used with tight encoding and
* if lossy updates are enabled so we can disable all the
* calculations otherwise */
if (!vs->lossy) {
vs->non_adaptive = true;
}
#ifdef CONFIG_VNC_TLS
if (acl && x509 && vs->tls.x509verify) {
if (!(vs->tls.acl = qemu_acl_init("vnc.x509dname"))) {

View File

@@ -81,8 +81,16 @@ typedef void VncSendHextileTile(VncState *vs,
#define VNC_MAX_WIDTH 2560
#define VNC_MAX_HEIGHT 2048
/* VNC_DIRTY_PIXELS_PER_BIT is the number of dirty pixels represented
* by one bit in the dirty bitmap */
#define VNC_DIRTY_PIXELS_PER_BIT 16
/* VNC_DIRTY_BITS is the number of bits in the dirty bitmap. */
#define VNC_DIRTY_BITS (VNC_MAX_WIDTH / 16)
#define VNC_DIRTY_BITS (VNC_MAX_WIDTH / VNC_DIRTY_PIXELS_PER_BIT)
/* VNC_DIRTY_BPL (BPL = bits per line) might be greater than
* VNC_DIRTY_BITS due to alignment */
#define VNC_DIRTY_BPL(x) (sizeof((x)->dirty) / VNC_MAX_HEIGHT * BITS_PER_BYTE)
#define VNC_STAT_RECT 64
#define VNC_STAT_COLS (VNC_MAX_WIDTH / VNC_STAT_RECT)